United Steel manufactures two types of steel at three different steel mills. During a given month, each steel mill has 200 hours of blast furnace time available. Because of differences in the furnaces at each mill, the time and cost to produce a ton of steel differ for each mill, as listed in the file P04_66.xlsx. Each month, the company must manufacture at least 500 tons of steel 1 and 600 tons of steel 2. Determine how United Steel can minimize the cost of manufacturing the desired steel.